The present invention relates to an apparatus for slitting a traveling corrugated paperboard sheet and, in particular, to a thin rotary blade slitting apparatus for substantially improving the quality of the slit.
Apparatus for longitudinally slitting a continuous traveling sheet or web of corrugated paperboard is well known in the art. Such apparatus is often combined with a mechanism for simultaneously providing longitudinal score lines to the advancing sheet, which score lines facilitate subsequent folding in the construction of boxes or the like. Thus, a combined "slitter-scorer" utilizes pairs of rotatable cutting tools and scoring tools disposed in the path of the advancing sheet, with one tool of each pair disposed on an opposite side of the sheet. Typically, multiple slitting tools are mounted coaxially and laterally spaced across the width of the sheet and, likewise, multiple scoring tools are also coaxially mounted and spaced across the sheet width.
In the prior art, each pair of upper and lower slitting tools is disposed with overlapping radial cutting edges between which the advancing paperboard sheet is moved to provide a continuous cut. Although the operation is commonly referred to as "slitting", the cutting tools in fact shear the moving sheet causing a relative vertical displacement of the cut edges from one another. As the thickness of the corrugated board being processed increases, the cuts tend to become more ragged, the edges tend to be crushed, and the cut quality tends to degrade significantly. Another problem commonly associated with rotary shear cutting of corrugated board is the generation of dust. Fine paper dust is a very serious problem which may result in clogged filters on air handling systems, hazardous air quality for workers, contamination of electronic and other equipment, and even explosion or fire hazards.
Other methods and apparatus for cutting corrugated paperboard have been developed to eliminate or alleviate some of the problems associated with rotary shear cutting. Thus, it is known to utilize high pressure water jets to cut paperboard. Water jets provide high quality cuts, but the equipment has an extremely high initial cost and requires costly maintenance.
U.S. Pat. No. 4,627,214 shows a slitter-scorer apparatus of one prior art construction in which the board is sheared by passage between the overlapping edges of a pair of rotary cutting knives. Even when such cutting knives are properly adjusted and maintained in a sharpened condition, their use to slit heavier double and triple wall board has been less than satisfactory.
There is a need, therefore, for an apparatus which will provide a clean, dust-free cut in an efficient and economical manner.